The Clinical Core's primary function is to provide patients and patient material for HD research projects within our program and our institution, and to investigators at other institutions. The Core accomplishes this by diagnosing and following approximately 300 well-characterized HD patients, many of whom are drawn from a representative Maryland sample first identified in 1980. Approximately 40 new patients according to a protocol developed for HD by the core staff. The protocol provides detailed documentation of time and mode of onset, neurological features, functional capacity, cognitive state, and psychiatric state. For this renewal, new patients will be MRI scanned at the time of diagnosis and every two years thereafter. Current clinical data are maintained in a database to facilitate research project PIs choosing patients appropriate to their protocols, and correlate their findings with clinical data. The Clinical core also facilitates the piloting of new research projects as opportunities arise, and core faculty carry out research on diagnosis and epidemiology. During the next funding period these research efforts will include: 1) development of standardized diagnostic criteria for general use in research classification; and 2) documentation of individual and familial variation in course of illness and the correlates of this variation. The latter will use the prospective, longitudinal data collected on the Maryland HD sample, ascertained during the first funding period. Finally, the clinical core is active in information transfer through publications, participation in lay organizations, and provision of clinical and research training in HD.